Towards a general perspective on life-history evolution and diversification in parasitoid wasps

In attempting to explain the marked interspecific variation evident in many components of life-history in parasitoid wasps, biologists have sought to identify general predictors of suites of ‘important’ life-history traits. Two predictors currently in general use are: (1) the parasitoid mode of larval development in relation to future host growth and development [no further host growth and development (= idiobiosis) versus continued host growth and development (= koinobiosis)]; and (2) the ovigeny index (the degree to which the lifetime potential complement of eggs is mature at the start of adult life in females). These have been postulated to share several life-history correlates, and an earlier comparative analysis showed the predictors to be associated. Two questions are thus posed: which life-history variables are actually common to both idio/koinobiosis and the ovigeny index, and which are responsible for the link between these two axes of life-history diversity? Through comparative analyses of a database of life-history traits for 133 parasitoid wasp species, four life-history correlates out of the 11 we investigated are shown to account for the association between the two predictors: the relative level of resource investment per egg (degree of yolk richness, which is lower in koinobionts), pre-adult lifespan (longer in koinobionts), female lifespan (shorter in koinobionts), and maximum egg load (larger in koinobionts). Our findings pave the way for full integration of the dichotomous hypothesis with the ovigeny index hypothesis, to provide a holistic perspective on parasitoid wasp life-history diversity and evolution